This invention relates to a device by which the end of an optical cable incorporated in a power cable unwindable from a drum is maintained fixed relative to an optical reader.
It is usual to equip mobile cranes, for example of overhead travelling type, and/or other similar means with large power cables. These are usually wound on large-diameter cable winding drums fixed to the crane body. Such cable winding drums are driven in such a manner that when the crane moves the power cable is unwound or wound as required.
It is known to insert in these power cables, in addition to the electrical feed cables, an optical cable for transmitting control signals (in the present context an optical cable is meant a single optical fiber or a bundle of fibers).
When the cable winding drum rotates it is notoriously difficult to read the signals present at the end of the optical cable which axially emerges from said cable winding drum and is hence in a state of axial rotation.
In this respect, for obvious reasons a brush system as for electric cables cannot be used, but instead devices designed ad hoc and known to the expert of the art have to be employed. However such devices all have considerable drawbacks, they being all of very complicated construction and/or of very high cost.
For example, one reader device for this use comprises a seat having a plurality of circularly arranged mirrors, the end of the axially rotating optical cable being inserted into this seat. In this manner while the cable rotates, the signals leaving the optical cable are reflected towards a final reader unit and can hence be read. It is apparent that devices of this type must be of very high precision and are therefore of very high constructional cost. Further drawbacks of such devices are signal power loss and distortion caused by the multiple reflection of the light ray before it reaches the final reader unit.